Is it possible to upgrade angularjs atttribute directives to use in angular 4?

Question

I've been able to upgrade an angularjs element directive to be used in angular 4. Here's a sample code:

[myScores.js]

angular.module('app.components.directives.myScores', [])
.directive('myScores', function() {
  return {
    scope: {
      score: '=',
    },
    template: '<div>&gt;&gt;&gt; Your score is {{score}} &lt;&lt;&lt;',
    link: function(scope) {
      console.log("in myScores", scope)
    }
  };
});

[myScores.ts]

import { Directive, ElementRef, Injector, Input, Output, EventEmitter } from '@angular/core';
import { UpgradeComponent } from '@angular/upgrade/static';

@Directive({
  selector: 'my-scores'
})
export class MyScoresDirective extends UpgradeComponent {
  @Input() score: number;

  constructor(elementRef: ElementRef, injector: Injector) {
    super('myScores', elementRef, injector);
  }
}

Notice I'm using UpgradeComponent to upgrade the myScores element directive. I've tried the same on an attribute directive but got an error. Is there a way to upgrade an attribute directive?

Here's my attempt of upgrading an attribute directive:

[makeGreen.js]

angular.module('app.components.directives.makeGreen', [])
.directive('makeGreen', function() {
  return {
    restrict: 'A',
    link: function(scope, element) {
      console.log("in makeGreen", scope)
      console.log("element", element)
      element.css('color', 'green');
    }
  };
});

[makeGreen.ts]

import { Directive, ElementRef, Injector, Input, Output, EventEmitter } from '@angular/core';
import { UpgradeComponent } from '@angular/upgrade/static';

@Directive({
  selector: '[makeGreen]'
})
export class MakeGreenDirective extends UpgradeComponent {
  @Input() count: number;
  @Output() clicked: EventEmitter<number>;

  constructor(elementRef: ElementRef, injector: Injector) {
    console.log("elementRef", elementRef.nativeElement)
    super('makeGreen', elementRef, injector);
  }
}

I get an error when loading a page that has something like:

<div makeGreen>Text should be green</div>

I got this error:

Error: Directive 'makeGreen' is not a component, it is missing template.

Answer 1

A Attribute directive can totally have the Input property which can be passed to it from the tag where it's used : For ex:

<p highlightThis [highlightColor]="'orange'" [count]="5">Highlighted in orange</p>

Also make sure your appModule/SharedModule imports it.

So the problem i see is with the way you are defining your structural directive. A structural directive doesn't have any template structure attached to it. It applies to any html tag where it's used.

For you case, i see you are extending the directive with Component class which is not acceptable to a Attribute directive :--

MakeGreenDirective extends UpgradeComponent {

You should keep the Attribute Directive separate from any Component. For Ex:

  import { Directive, ElementRef, Injector, Input, Output, EventEmitter } from 
  '@angular/core';

  @Directive({
    selector: '[highlightThis]'
   })

 export class HighLightThisDirective {
 @Input() count: number;
 @Input() highlightColor: string;
 @Output() clicked: EventEmitter<number>;

 constructor(private elementRef: ElementRef, injector: Injector) {  }

 ngOnInit(): void {
   this.decorateMyTag();
 }

 private decorateMyTag(): void {
   console.log("highlightColor", this.highlightColor);
   this.elementRef.nativeElement.style.backgroundColor = this.highlightColor;
  }
}